1. Field of the Invention
The present invention relates to a method of manufacturing a toner.
2. Description of the Related Art
An electrophotographic image forming apparatus comprises an image forming process mechanism including: a photoreceptor; a charging section for charging a photoreceptor surface; an exposing section for irradiating with signal light the photoreceptor surface being charged, to form thereon an electrostatic latent image corresponding to image information; a developing section for supplying a toner contained in a developer to the electrostatic latent image formed on the photoreceptor surface, to form thereon a toner image; a transfer section provided with a transfer roller for transferring the toner image from the photoreceptor surface to a recording medium; a fixing section provided with a fixing roller for fixing the toner image onto the recording medium; and a cleaning section for cleaning the photoreceptor surface from which the toner image has been transferred. In the electrophotographic image forming apparatus, the electrostatic latent image is developed by use of a one-component developer containing a toner as a developer or by use of a two-component developer containing toner and carrier as developers so that an image is formed. Through the electrophotographic image forming apparatus, an image of favorable image quality can be formed at high speed and low cost. This promotes the use of the electrophotographic image forming apparatus in a copier, a printer, a facsimile, or the like machine, resulting in a remarkable spread thereof in recent years. Simultaneously, the image forming apparatus has faced up to more demanding requirements. Among such requirements, particular attentions are directed to enhancement in definition and resolution, stabilization of image quality, and an increase in image forming speed, regarding an image being formed by the image forming apparatus. In order to fulfill these demands, a two-way approach is indispensable in view of both the image forming process and the developer. Regarding the enhancement in definition and resolution of the image, the reduction in diameter of toner particles is one of problems to be solved from the aspect of the developer. This is based on the perspective such that it is important to authentically reproduce the electrostatic latent image.
Conventionally, a pulverization method, a polymerization method, a wet method, and the like method have been known as a method of manufacturing a toner. According to the pulverization method, an admixture of toner raw materials such as binder resin and a colorant is melt-kneaded, and a melt-kneaded product thus obtained is cooled down to be solidified, followed by pulverization and classification, in a consequence whereof a toner is obtained. The diameter-reduced toner manufactured by the pulverization method contains particles of which shapes are not uniform, and has an extremely deteriorated powder flowability. When such a toner is used, the toner is unevenly charged before supplied to an electrostatic latent image, for example, which possibly generates unevenness in density or color of an image being formed. According to the polymerization method, a monomer compound of binder resin, a colorant, and the like ingredients are evenly mixed in a solvent, followed by polymerization of the monomer compound of binder resin, in a consequence whereof a toner is obtained. The polymerization method has a drawback such that the binder resin is limited to vinylic polymers such as polyvinyl chloride, which can be manufactured by radical polymerization. The toner containing the vinylic polymer as binder resin is inferior to a toner containing polyester as binder resin, in terms of a fixing property onto a recording medium, transparency, and the like properties. According to the wet method, in a solvent containing an organic solvent, mixed are fine synthetic resin particles, a colorant, and other toner raw materials which are then coagulated, and a coagulated product thus obtained is heated, in a consequence whereof a toner is obtained. When the wet method is implemented in industrial scale, a large amount of waste liquid containing organic solvent is generated. Considering environmental problems, the waste liquid should not be disposed without treatment. Accordingly, there arises a need of establishing a large-scale disposing facility for collecting the organic solvent, resulting in a higher cost for manufacturing a toner as compared to the other methods.
Conventionally, various methods have been known how to manufacture a toner by applying a shearing force to the toner raw material in water. For example, there has been proposed a toner manufacturing method in which a polymeric monomer composition containing a polymeric monomer, a colorant, and a polymeric initiator is added under a shearing force to a water dispersion (of which pH is from 6.5 to 12) containing inorganic dispersants such as phosphoric salt, carbonate, hydroxide, sulfate, bentonite, silica, and alumina, and then mixed to obtain an admixture that is further subjected to a shearing force to thereby granulate the polymeric monomer composition, followed by suspension polymerization of granulated substances thus obtained, in a consequence whereof a toner is obtained (refer to, for example, Japanese Unexamined Patent Publication JP-A 10-312086 (1998)). Further, there has been proposed a toner manufacturing method in which a polymeric monomer composition containing a polymeric monomer and a colorant is added to a water dispersion containing an inorganic dispersant, and then mixed to obtain an admixture that is further subjected to a shearing force, a collision force, etc., to thereby granulate the polymeric monomer composition, followed by suspension polymerization of granulated substances thus obtained, in a consequence whereof a toner is obtained (refer to, for example, Japanese Unexamined Patent Publication JP-A 8-305084 (1996)). Regarding the toner manufacturing method in which a polymeric monomer composition containing a polymeric monomer and a colorant is added to a water dispersion containing an inorganic dispersant, and then mixed to thereafter granulate the polymeric monomer composition, followed by suspension polymerization of granulated substances thus obtained, in a consequence whereof a toner is obtained, there has been proposed that the polymeric monomer composition is granulated by means of a granulator comprising: an open-air cylindrical container; a spinning rotor which is provided in an internal space of the cylindrical container and supported on one face in a thickness direction of the cylindrical container so as to be rotatable, having a shaft center in common with the cylindrical container; a following screen having a shape of tube or bottomed tube, which has a shaft center in common with the cylindrical container and is provided around the spinning rotor so as to be rotatable with rotation of the spinning rotor, and of which peripheral wall is provided with a plurality of slits for flowing a liquid; and a fixed screen having a shape of tube or bottomed tube, which has a shaft center in common with the cylindrical container and is provided around the following screen, and of which peripheral wall is provided with a plurality of slits for flowing a liquid (refer to, for example, Japanese Unexamined Patent Publication JP-A 2-32363 (1990)). The granulator used in the method disclosed by JP-A 2-32363 is commercially available, and known granulator includes Ebara milder (trade name) manufactured by Ebara Corporation.
In those techniques disclosed in JP-A 10-312086, JP-A 8-305084, and JP-A 2-32363, a toner is obtained by adding the polymeric monomer composition to the water dispersion containing the inorganic dispersant, and then applying the shearing force, the collision force, etc. to granulate the polymeric monomer composition, followed by the suspension polymerization of the granulated substances. The inorganic dispersant has a function to prevent bubbles which have actions of coagulating and coarsening the toner, from arising upon application of the shearing force. In those techniques, however, the generation of bubbles cannot be sufficiently prevented, so that a part of the obtained toner is coarsened, resulting in uneven particle diameter and shape of the toner. Thus, those techniques have a drawback that a diameter-reduce toner as desired cannot be obtained. Furthermore, another known method is a fusion emulsification method in which a toner is manufactured by applying a shearing force to a melt-kneaded product of toner raw materials in water. Also for the method, a technical improvement has been desired to obtain a toner having a further reduced diameter.